• Steel and Composite Structures
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• v.34 no.2
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• pp.279-288
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• 2020

The computational post-buckling strength of the tilted sandwich composite shell structure is evaluated in this article. The computational responses are obtained using a mathematical model derived using the higher-order type of polynomial kinematic in association with the through-thickness stretching effect. Also, the sandwich deformation behaviour of the flexible soft-core sandwich structural model is expressed mathematically with the help of a generic nonlinear strain theory i.e. Green-Lagrange type strain-displacement relations. Subsequently, the model includes all of the nonlinear strain terms to account the actual deformation and discretized via displacement type of finite element. Further, the computer code is prepared (MATLAB environment) using the derived higher-order formulation in association with the direct iterative technique for the computation of temperature carrying capacity of the soft-core sandwich within the post-buckled regime. Further, the nonlinear finite element model has been tested to show its accuracy by solving a few numerical experimentations as same as the published example including the consistency behaviour. Lastly, the derived model is utilized to find the temperature load-carrying capacity under the influences of variable factors affecting the soft-core type sandwich structural design in the small (finite) strain and large deformation regime including the effect of tilt angle.

• Polymer(Korea)
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• v.38 no.1
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• pp.80-84
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• 2014

Polymer nanoparticles with cross-linked core and PBA/PS double-shell were synthesized and their baroplastic properties were characterized. PBA/PS, the inner and outer shell with cross-linked core consisting of St and DVB were synthesized by three-stage emulsion polymerization. The obtained materials exhibited pressure-induced mixing of their components and could be processed at $25^{\circ}C$ by compression molding which means there was no effect of the presence of cross-linked core. Interestingly, the Young's modulus of molded objects has found to be affected strongly by the size of double-shell nanoparticles. Furthermore, the molded object of higher PBA content was successfully recycled 5 times at $25^{\circ}C$ and showed 0.55 MPa of modulus and 1.81 MPa of strength at break.

• Structural Engineering and Mechanics
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• v.86 no.2
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• pp.157-165
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• 2023

In the present work, the vibration characteristics of sandwich nanocomposite shells, fortified with graphene platelets (GPLs) have been researched. The shell has been considered as the stadium roof shape with double curvatures under vibration due to earthquake. The nanocomposite has the matrix of concrete which is fortified with uniform or linear dispersions of GPLs. Also, the core possesses cellular type square architecture for which the effective elastic modulus has been defined in the context of relative density based relations. Based upon the classic shell strains containing two identical curvatures, the governing equations have been established and solved through differential quadrature approach. It will be seen that the vibrational frequencies rely on the core relative density, height of layers, the amount and dispersions of GPLs and even shell geometric parameters.

• Bulletin of the Korean Chemical Society
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• v.25 no.7
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• pp.1025-1030
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• 2004

A hybrid linear polymer-dendrimer block copolymer, poly(ethylene glycol)-block-poly(L-lysine) dendrimer, was synthesized and introduced to form polyionic complexes with DNA. The copolymer formed core-shell type nanoparticles with plasmid DNA. From dynamic light scattering experiments, the mean diameter of the polyplexes was observed to be 154.4 nm. The complex showed much increased water solubility compared to poly(L-lysine). The plasmid DNA in polyplexes was efficiently protected from the enzymatic digestion of DNase I. The cytotoxicity and transfection efficiency for 293 cells was measured in comparison with poly(Llysine).

• Journal of the Korean Applied Science and Technology
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• v.21 no.3
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• pp.259-266
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• 2004

Film properties of monodispersed model composite latexes with particle size of 190 nm, which consist of n-butyl acrylate as a soft phase monomer and methyl methacrylate as a hard phase monomer with different morphology was examined. Five different types of model latexes were used in this study such as random copolymer particle, soft-core/hard-shell particle, hard-core/soft-shell particle, gradient type particle, and mixed type particle. Tensile strength and tensile elongation at break of final films were evaluated. Those properties can be interpreted in terms of PBA/PMMA phase ratio and their morphology. The interfacial adhesion strength was also evaluated using $180^{\circ}$ peel strength measurement and cross hatch cutting test.

• Journal of the Korean Applied Science and Technology
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• v.21 no.2
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• pp.132-139
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• 2004

Film forming behavior of monodispersed model composite latexes with particle size of 190 nm, which consist of n-butyl acrylate as a soft phase monomer and methyl methacrylate as a hard phase monomer with different morphology was examined. Five different types of model latexes were used in this study such as random copolymer particle, soft-core/hard-shell particle, hard-core/soft-shell particle, gradient type particle, and mixed type particle. The film forming behavior was evaluated using pseudo on-line measurements of the cumulative weight loss, the UV transmittance, and the tensile fracture energy. Each stages of film formation I, II were not sensitive to the morphology of model latexes, but stage-ill was largely dependent on the morphology of model latexes. The chain mobility of polymer which composed the shell component was found to dominantly determine the behavior of film forming stage-III.

• Journal of the Korean Ceramic Society
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• v.54 no.3
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• pp.222-227
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• 2017

Flake-type micro hollow silica was synthesized by precipitation method using an $Mg(OH)_2$ inorganic template and sodium silicate and ammonium sulfate as the silica precursors. We investigated the effects of the silica precursor concentration on the shape, shell thickness, and surface of the hollow silica. When the concentration of the silica precursor was 0.5 M, the hollow silica had a smooth and translucent thin shell, but the shell was broken. On the other hand, the shell thickness of the hollow silica changed in the range of 12 nm to 18 nm with the increase of the precursor concentration from 0.7 M to 1.1 M. Simultaneously, unintended spherical silica satellites were created on the shell surface. The number of satellites and the size rose according to the increased concentration of silica precursor. The reason for the formation of spherical silica satellites is that the $NH_4OH$ nucleus generated in the synthesis of hollow silica acted as another silica reaction site.

• Bulletin of the Korean Chemical Society
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• v.35 no.2
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• pp.575-580
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• 2014

We uniformly coated Eu(III)- and Tb(III)-doped yttrium oxide onto the surface of $SiO_2$ spheres and then characterized them by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction crystallography and UV-Visible absorption. 2D and 3D photoluminescence image map profiles were reported for the core-shell type structure. Red emission peaks of Eu(III) were observed between 580 to 730 nm and assigned to $^5D_0{\rightarrow}^7F_J$ (J = 0 - 4) transitions. The green emission peaks of Tb(III) between 450 and 650 nm were attributed to the $^5D_4{\rightarrow}^7F_J$ (J = 6, 5, 4, 3) transitions. For annealed samples, Eu(III) ions were embedded at a $C_2$ symmetry site in $Y_2O_3$, which was accompanied by an increase in luminescence intensity and redness, while Tb(III) was changed to Tb(IV), which resulted in no green emission.

• Korean Journal of Materials Research
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• v.20 no.1
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• pp.25-30
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• 2010

Si nanowire/multiwalled carbon nanotube nanocomposite arrays were synthesized. Vertically aligned Si nanowire arrays were fabricated by Ag nanodendrite-assisted wet chemical etching of n-type wafers using $HF/AgNO_3$ solution. The composite structure was synthesized by formation of a sheath of carbon multilayers on a Si nanowire template surface through a thermal CVD process under various conditions. The results of Raman spectroscopy, scanning electron microscopy, and high resolution transmission electron microcopy demonstrate that the obtained nanocomposite has a Si nanowire core/carbon nanotube shell structure. The remarkable feature of the proposed method is that the vertically aligned Si nanowire was encapsulated with a multiwalled carbon nanotube without metal catalysts, which is important for nanodevice fabrication. It can be expected that the introduction of Si nanowires into multiwalled carbon nanotubes may significantly alter their electronic and mechanical properties, and may even result in some unexpected material properties. The proposed method possesses great potential for fabricating other semiconductor/CNT nanocomposites.

• Structural Engineering and Mechanics
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• v.77 no.1
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• pp.57-74
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• 2021

The thermal eigenvalue responses of the graded sandwich shell structure are evaluated numerically under the variable thermal loadings considering the temperature-dependent properties. The polynomial type rule-based sandwich panel model is derived using higher-order type kinematics considering the shear deformation in the framework of the equivalent single-layer theory. The frequency values are computed through an own home-made computer code (MATLAB environment) prepared using the finite element type higher-order formulation. The sandwich face-sheets and the metal core are discretized via isoparametric quadrilateral Lagrangian element. The model convergence is checked by solving the similar type published numerical examples in the open domain and extended for the comparison of natural frequencies to have the final confirmation of the model accuracy. Also, the influence of each variable structural parameter, i.e. the curvature ratios, core-face thickness ratios, end-support conditions, the power-law indices and sandwich types (symmetrical and unsymmetrical) on the thermal frequencies of FG sandwich curved shell panel model. The solutions are helping to bring out the necessary influence of one or more parameters on the frequencies. The effects of individual and the combined parameters as well as the temperature profiles (uniform, linear and nonlinear) are examined through several numerical examples, which affect the structural strength/stiffness values. The present study may help in designing the future graded structures which are under the influence of the variable temperature loading.